linux-kernel - Re: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core

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Message-ID: <5721DDE5.7060708@ti.com>
Date:	Thu, 28 Apr 2016 12:54:45 +0300
From:	Roger Quadros <rogerq@...com>
To:	Jun Li <jun.li@....com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"balbi@...nel.org" <balbi@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"peter.chen@...escale.com" <peter.chen@...escale.com>
CC:	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"abrestic@...omium.org" <abrestic@...omium.org>,
	"r.baldyga@...sung.com" <r.baldyga@...sung.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core

Hi,

On 27/04/16 14:22, Roger Quadros wrote:
> On 26/04/16 03:07, Jun Li wrote:
>> Hi
>>
>>> -----Original Message-----
>>> From: Roger Quadros [mailto:rogerq@...com]
>>> Sent: Monday, April 25, 2016 10:04 PM
>>> To: Jun Li <jun.li@....com>; stern@...land.harvard.edu; balbi@...nel.org;
>>> gregkh@...uxfoundation.org; peter.chen@...escale.com
>>> Cc: dan.j.williams@...el.com; jun.li@...escale.com;
>>> mathias.nyman@...ux.intel.com; tony@...mide.com; Joao.Pinto@...opsys.com;
>>> abrestic@...omium.org; r.baldyga@...sung.com; linux-usb@...r.kernel.org;
>>> linux-kernel@...r.kernel.org; linux-omap@...r.kernel.org
>>> Subject: Re: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core
>>>
>>> Hi,
>>>
>>> On 21/04/16 09:38, Jun Li wrote:
>>>> Hi,
>>>>
>>>> ...
>>>>>
>>>>>  /**
>>>>> + * usb_gadget_start - start the usb gadget controller and connect to
>>>>> +bus
>>>>> + * @gadget: the gadget device to start
>>>>> + *
>>>>> + * This is external API for use by OTG core.
>>>>> + *
>>>>> + * Start the usb device controller and connect to bus (enable pull).
>>>>> + */
>>>>> +static int usb_gadget_start(struct usb_gadget *gadget) {
>>>>> +	int ret;
>>>>> +	struct usb_udc *udc = NULL;
>>>>> +
>>>>> +	dev_dbg(&gadget->dev, "%s\n", __func__);
>>>>> +	mutex_lock(&udc_lock);
>>>>> +	list_for_each_entry(udc, &udc_list, list)
>>>>> +		if (udc->gadget == gadget)
>>>>> +			goto found;
>>>>> +
>>>>> +	dev_err(gadget->dev.parent, "%s: gadget not registered.\n",
>>>>> +		__func__);
>>>>> +	mutex_unlock(&udc_lock);
>>>>> +	return -EINVAL;
>>>>> +
>>>>> +found:
>>>>> +	ret = usb_gadget_udc_start(udc);
>>>>> +	if (ret)
>>>>> +		dev_err(&udc->dev, "USB Device Controller didn't start: %d\n",
>>>>> +			ret);
>>>>> +	else
>>>>> +		usb_udc_connect_control(udc);
>>>>
>>>> For drd, it's fine, but for real otg, gadget connect should be done by
>>>> loc_conn() instead of gadget start.
>>>
>>> It is upto the OTG state machine to call gadget_start() when it needs to
>>> connect to the bus (i.e. loc_conn()). I see no point in calling gadget
>>> start before.
>>>
>>> Do you see any issue in doing so?
>>
>> This is what OTG state machine does:
>> case OTG_STATE_B_PERIPHERAL:
>>      otg_chrg_vbus(otg, 0);
>>      otg_loc_sof(otg, 0);
>>      otg_set_protocol(fsm, PROTO_GADGET);
>>      otg_loc_conn(otg, 1);
>>      break;

On second thoughts, after seen the OTG state machine.
otg_set_protocol(fsm, PROTO_GADGET); is always followed by otg_loc_conn(otg, 1);
And whenever protocol changes to anything other the PROTO_GADGET, we use
otg_loc_conn(otg, 0);

So otg_loc_conn seems redundant. Can we just get rid of it?

usb_gadget_start() implies that gadget controller starts up and enables pull.
usb_gadget_stop() implies that gadget controller disables pull and stops.


Can you please explain why just these 2 APIs are not sufficient for full OTG?

Do we want anything to happen between gadget controller start/stop and
pull on/off?

cheers,
-roger

>>
>> You intend to abstract something common in this api when start gadget,
>> which should be called by otg_set_protocol(fsm, PROTO_GADGET); and
>> drd_set_protocol(fsm, PROTO_GADGET); right?
>>
>> So you may move usb_udc_connect_control(IMO usb_gadget_connect()
>> is better)out of usb_gadget_start(), then for drd:
>>
>> case OTG_STATE_B_PERIPHERAL:
>>      drd_set_protocol(fsm, PROTO_GADGET);
>>      otg_drv_vbus(otg, 0);
>>      usb_gadget_connect();
> 
> OK. I understand now. I'll implement your suggestion. Thanks.
> 
> cheers,
> -roger
> 
>>>>
>>>>> +
>>>>> +	mutex_unlock(&udc_lock);
>>>>> +
>>>>> +	return ret;
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * usb_gadget_stop - disconnect from bus and stop the usb gadget
>>>>> + * @gadget: The gadget device we want to stop
>>>>> + *
>>>>> + * This is external API for use by OTG core.
>>>>> + *
>>>>> + * Disconnect from the bus (disable pull) and stop the
>>>>> + * gadget controller.
>>>>> + */
>>>>> +static int usb_gadget_stop(struct usb_gadget *gadget) {
>>>>> +	struct usb_udc *udc = NULL;
>>>>> +
>>>>> +	dev_dbg(&gadget->dev, "%s\n", __func__);
>>>>> +	mutex_lock(&udc_lock);
>>>>> +	list_for_each_entry(udc, &udc_list, list)
>>>>> +		if (udc->gadget == gadget)
>>>>> +			goto found;
>>>>> +
>>>>> +	dev_err(gadget->dev.parent, "%s: gadget not registered.\n",
>>>>> +		__func__);
>>>>> +	mutex_unlock(&udc_lock);
>>>>> +	return -EINVAL;
>>>>> +
>>>>> +found:
>>>>> +	usb_gadget_disconnect(udc->gadget);
>>>>
>>>> Likewise, gadget disconnect also should be done by loc_conn() instead
>>>> of gadget stop.
>>>>
>>>>> +	udc->driver->disconnect(udc->gadget);
>>>>> +	usb_gadget_udc_stop(udc);
>>>>> +	mutex_unlock(&udc_lock);
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>
>>>> Li Jun
>>>>
> --
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